Hydraulic steering system

Abstract

A hydraulic steering system ( 1 ) with a supply connection arrangement, having a high-pressure connection (P) and a low-pressure connection (T), and with a working connection arrangement (L, R), a directional valve ( 2 ) and a metering pump unit ( 3, 4 ) being arranged between the supply connection arrangement and the working connection arrangement, the metering pump arrangement having at least two hydraulically parallel-connected and mechanically parallel-operated metering pumps ( 3, 4 ) with a shut-off valve ( 6 ) in a hydraulic connection between the two metering pumps ( 3, 4 ), said shut-off valve ( 6 ) having a return spring ( 16 ) and a first control inlet ( 15 ) that is connected with the high-pressure connection (P).

What is claimed is:  
     
       1. A hydraulic steering system with a supply connection arrangement, having a high-pressure connection and a low-pressure connection, and with a working connection arrangement, a directional valve and a metering pump unit being arranged between the supply connection arrangement and the working connection arrangement, the metering pump arrangement having at least two hydraulically parallel-connected and mechanically parallel-operated metering pumps with a shut-off valve in a hydraulic connection between the two metering pumps, said shut-off valve having a return spring and a first control inlet that is connected with the high-pressure connection, characterized in that the shut-off valve ( 6 ) has a second steering inlet ( 17 ), which can be acted upon by a pressure from a lowest-pressure connection (T 0 ). 
     
     
       2. The steering system according to  claim 1 , characterized in that the pressure at the second steering inlet ( 17 ) acts in the same direction as the return spring ( 16 ). 
     
     
       3. The steering system according to  claim 1 , characterized in that a non-return valve ( 11 ) prestressed with low opening pressure is arranged in high-pressure line ( 8 ) connected with the high-pressure connection (P), a steering line ( 14 ) branching off to the first steering connection ( 15 ) in front of said valve ( 11 ). 
     
     
       4. The steering system according to  claim 3 , characterized in that the opening pressure is maximum 1 bar. 
     
     
       5. The steering system according  claim 1 , characterized in that the second steering inlet ( 17 ) is connected with a change-over valve ( 19 ), which connects the second steering inlet ( 17 ) with either the lowest-pressure connection (T 0 ) or the high-pressure connection (P). 
     
     
       6. The steering system according to  claim 5 , characterized in that the changeover valve ( 19 ) can be remote-controlled. 
     
     
       7. The steering system according to  claim 5 , characterized in that the changeover valve ( 19 ) is a solenoid valve. 
     
     
       8. The steering system according to  claim 5 , characterized in that the disconnectable metering pump ( 4 ) has at least threefold the displacement of the other metering pump ( 3 ). 
     
     
       9. The steering system according to  claim 1 , characterized in that the shut-off valve ( 6 ) has a slide ( 24 ), which, together with a distributor plate ( 22 ) closed in the area of the slide ( 24 ) and a housing ( 23 ) surrounding the slide ( 24 ), borders a low-pressure chamber ( 26 ). 
     
     
       10. The steering system according to  claim 9 , characterized in that the low-pressure chamber ( 26 ) is sealed in relation to all hydraulic lines. 
     
     
       11. The steering system according to  claim 10 , characterized in that the slide ( 24 ) has a sealing ( 28 ), which is displaceable together with the slide ( 24 ) in relation to the housing ( 23 ). 
     
     
       12. The steering system according to  claim 9 , characterized in that a lowest-pressure channel ( 29 ;  36 ,  37 ) is provided in the housing ( 23 ), which ends in the low-pressure chamber ( 26 ) in the area of the distributor plate ( 22 ). 
     
     
       13. The steering system according to  claim 12 , characterized in that a recess ( 39 ) surrounding the low-pressure chamber ( 26 ) is arranged between the distributor plate ( 22 ) and the housing ( 23 ), the lowest-pressure channel ( 36 ,  37 ) ending in said recess ( 39 ). 
     
     
       14. The steering system according to  claim 13 , characterized in that a first section ( 36 ) of the lowest-pressure channel ( 36 ,  37 ) extends perpendicularly to the distributor plate ( 22 ). 
     
     
       15. The steering system according to  claim 14 , characterized in that the lowest-pressure channel has a second section ( 37 ), which extends radially to the movement direction of the slide ( 24 ).